An interesting question came up the other day: What exactly does the sendmail daemon do with SMTP sessions that are in progress when it needs to restart?
For the purpose of discussion, let's assume that it's being restarted via
service sendmail restart. I'll wait a moment for admins to scream at their monitors about this . . .
More information than you ever wanted to know about sendmail debugging
Author's note: this is an older article I brought over from my prior blog by popular request. Some of the information may be a little dated.
The problem: You need to troubleshoot low-level details concerning a deferred message in sendmail but don't want to necessarily increase global log levels (or restart services).. . .